Salicylic acid ester as color inhibitor for polyester-monomer resins



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SALICYLIC cn) ESTER s coLoR INHIBITOR 5 FOR POLYESTER-MONOMER RESINS scan-115s. (C11 zed-145.4

This invention relates to interpolym'ers or, (A) 'ia1 es ers er dicar'boxylic acids-and dih'ydr'ic ale] ol sj'arid (B) monomers which are soluble in, C r Compatible with saidpolyesters and which contain a C=LCHg The invention has particular relati'oii' to interpo able mixtures of the" foregoing type, or the products of interpo'lymerization derived therefrom, whicli'liave" a relattively high resistance to 'dijscoloration'upori aging; a,

A. very'common resinifiable composition en joying' an extensive and rapidly increasing popularity comprises mixtures of (A) polyesters of alpha-beta ethylenicall'yud' saturated dicarboxylic acids such as maleic or fumaric acids and glycols' such as propylene glycol or diethylene glycol and (B) monomers, such asstyrene or vinyl ace tate,- containing C=CH2 groups, preferably, attached to a negativeradical, said monomers beingc'orn'patible with and interpolymerizable with said polyesters. These interpolynierizable mixtures are liquid and can readily. be poured into moldsor'spre'ad upon, or impregnated fabrics and mats of fibers of various types. Tlie'mix tures, when so applied, can easily be cured. bya heating or'baking operation in the absence of, or substantial ab: sence of externally applied pressures, to tdrmihard and strong resinous bodies of high utility. These bodies, in the absenceof added opacifying materials of coloring 40 matter such as pigments or other fillers, are clear and of but little or no color. Forthese reasons, they are of exceptional merit for the-main rame" of} transparent articles, such as tra'n'spar entsheets, airplane caiiopiesi or windows and manyother uses} 7. p p v v f Whiletheseproducts are highly serv'ic abf "ari extensive and growing use," they areicharacte'r'izifi slight" tendency to" undergof discoloration for yell M upon aging, especially if s'uch aging includes-e Q8511)? exposure to ultra violetirradiation'. l niorderito'redlic e the tendency of "the foregoing iiiter'polyrri todiscolor, has heretofore beens ugge ed porate into the-mixturespriortc the'icurmg op ratro certain compounds termedlightstabilizers;'whieh-hai e"a: capacity for reducing the tendeiicyot" theflniat er'ials' to discolor upon aging, but wh i chi in other'respects dojnot 1 substantially" affect the properties of the rri'ate'rials F 7 k This "invention is based upon the discovery thatertain esters'of salicylic acid are'hi'ghly" effective as 'lih lizeis in theforegoing;interpolymei'iiable mixtures The? aromatic"'esters,' or the 1ower1aliphatir gan; wh're a benzene rin'goran aliphatic group is directly j the oxygen bridge of the 5 ester, are; preferred 1 an f are represented byi lsobutyi salicylate A salicylic acid esters'uch"as pheiiyl salieylate isrela 2,773,049 Patented Dec. 4, 1956 2 tiye lyinexpensive to obtain and possesses a high degree of ,solubilityjin the interpolymerizable mixture, or the polyester constituting a base resin therein, so that it can eadilybc introduced into the mixture to be stabilized, either hot or cold.

The interpolymerizable mixtures, with which the salicylic esters maybe employed to increase light stability, comprise a relatively large and well-known class. The base component usually comprises, as previously indicated, a polyester of a glycol such as diethylene glycol,

I propylene glycol or polyethylene glycol and one or a plurality of dicarboxylic acids, at" least a portion of which embody an ethylenic group in alpha-beta relationship with respect to at least one of the carboxyls, fAci ds' of this latter type comprise maleic aci'dand' fum a'ri'c acid in most resins. However, the inventio includes the use of many other acids containing the group:

Numerous polyesters and the mode of preparing the same are discussed in Patent 2,593,787 to Earl B. Parker issued April 22, 1952. As indicated in the patent, the polyester components may and as a matter of fact, usuallydo contain a dicarboxylic acid componentwhich' is free of ethylenic unsaturation, or other types of unsaturation which react by addition with C=CHg groupsl Examples of such acids are phthalic acid, terephthalicacid, or the saturated aliphatic dicarboxylic acidsof the class re presented by succi'riic acid, adipic' acid, sebacic acid, az elaiic' acid, and the like. The invention also includesthe use of dicarboxylic acids of the foregoing types in'which one or more of the hydrogens of the rings or hydrocarbon chains arereplace'd by halogena toms such as chlorine,or byemethyl or ethyl groups, or other non functioning groups; When they are employed, the proportion of saturated or non-ethylenic acids may vary over a broad range, e'.'-g., 0.25 to 12 moles per mole of ethylenically unsaturated acids. 7 I

The preparation of the polyesters hasnow beenwell conventionalizedand' many of them constitute well'recognizedcomme'rcial products. Accordingly, the preparation'ofth'epolyester component does not require elabora-j tion'." It is s'uflic'ient to state that the polyester can readily be 'pre'paredby heating a mixture of a dihydric alcohol such as propylene glycol or diethylene glycol with' the di'carb'oxylic'acid or mixture of dicarboxylic acids in'the presence of or absence of a catalyst of esterification such as litharge or an aromatic sulfonic acid Usually; the

re'actionisconductedunder an inertatrriosphere suchas an atmosphere of carbon dioxide or-nitrogen. A'small amount of a solvent medium such as' x'ylene or toluene may be included. This solvent may-be-subjected-tore fiux' -distillat ion in which it operates? azeotropically to remove water of reaction whichcan be condensed, separated mechanically from the solvent medium and the latter returned tothe reac'tion'mixture. The temperature of reaction normally is such as will produce esterification reaction at a reasonable rate, as can readily' be determincdby the evolution of water from the system. A temperature of about to 250 C., moreor'lessiis' quiteeifective. The reactionis continued until apolyester-having'an acid value in a reasonable" range, e. g., 3 'to'abou't 50 is obtained. The polyester will usually be a'very viscous or even solidproduct at normal atmosp'her'ic" temperatures. The reaction usuallyiis completed in'a' period of about 2' to 20 hours. In no event isj the reactioncontinued so longas to produce an infusible insoluble product. I I t p In conducting'the reaction, the polyhydric alcohol corn; porrent is employed in stoi'chiornetric, or inslightly higher proportion! 5"or IOpe-rcen't by weight excess) with respect to-the sum of the carboxylic acid components:

2,773,049 r a t i Monomers suitable for use to provide an interpolymerizable mixture inaccordance with the provisions of this invention are disclosed in the foregoing patent to Earl E. Parker. Preferred monomers are liquids containing a. C=CHz group attached to a negative radical and are soluble in, or compatible with the polyester component. V

Styrene and styrene-like materials involving a C=CH2 group in a side chain attached to a benzene ring constitute an especially important class of monomers but esters and halides and other derivatives containing terminal C=CH2 groups are also effective for some applications. An appropriate list of the more common monomers is as follows:

TABLE A 1. Styrene 2. Alpha-methyl styrene 3. p-Methyl styrene 4. Divinyl benzene 5. Vinyl toluene Unsaturated esters such as:

Naturally, these are by no means comprehensive of the class but rather are in the nature of illustrations.

The monomers may conveniently be selected from those listed in the foregoing patent or they may be selected from the following general list:

(1) Monoolefinic hydrocarbons, that is, monomers containing only atoms of hydrogen and carbon, such as styrene, alpha-methyl styrene, alpha-ethyl styrene, alphabutyl styrene and vinyl toluene, and the like;

(2) Halogenated monoolefinic hydrocarbons, that is, monomers containing carbon, hydrogen and one or more halogen atoms such as alpha-chlorostyrene, alpha-bromostyrene, 2,5-dichlorostyrene, 2,5-dibromostyrene, 3,4-dichlorostyrene, 3,4-difiuorostyrene, ortho-, meta-, and para-fiuorostyrenes, 2,6-dichlorostyrene, 2,6-difluorostyrene, 3-fluoro-4-chlorostyrene, 3-chloro-4-fiuorostyrene, 2,4,5-trichlorostyrene, dichloromonofiuorostyrenes, ch1oroethylene (vinyl chloride), 1,1-dichloroethylene (vinyl- -alpha-chloroacetate and isopropenyl alpha-bromopropion ate;

Vinyl alpha-chloroacetate, vinyl alpha-bromoacetate, vinyl alpha-chloropropionate, vinyl alpha-bromopropionate, vinyl alpha-iodopropionate, vinyl alpha-chlorobutyrate, vinyl alpha-chlorovalerate and vinyl alpha-bromovalerate;

Allyl chlorocarbonate, allyl formate, allyl acetate, allyl propionate, allyl butyrate, allyl valerate, allyl caproate, diallyl phthalate, diallyl succinate, diethylene glycol bis- (allyl-carbonate), allyl 3,5,5-trimethylhexoate, allyl benzoate, allyl acrylate, allyl crotonate, allyl oleate, allyl chloroacetate, allyl trichloroacetate, allyl chloropropionate, allyl chlorovalerate, allyl lactate, allyl pyruvate, allyl aminoacetate, allyl acetoacetate, allyl thioacetate, diallyl- 3,4,5,6,7,7-hexachoro A4 endomethylene tetrahydrophthalate, as well as methallyl esters corresponding to the above allyl esters, as well as esters from such alkenyl alcohols as beta-ethyl allyl alcohol, beta-propyl allyl alcohol, 1- buten-4-ol, 2-methyl-buten-1-ol-4, 2(2,2-dimethylpropyl)- 1-buten-4-ol and l-pentene-4-ol;

Methyl alpha-chloroacrylate, methyl alpha-bromoacrylate, methyl alpha-fluoroacrylate, methyl alpha-iodoacrylate, ethyl alpha-chloroacrylate, propyl alpha-chloroacrylate, isopropyl alpha-bromoacrylate, amyl alpha-chloroacrylate, octyl alpha-chloroacrylate, 3,5,5-trimethylhexyl alpha-chloroacrylate, decyl alpha-chloroacrylate, methyl alpha-cyano acrylate, ethyl alpha-cyano acrylate, amyl alpha-'cyano acrylate and decyl alph-cyano acrylate;

Dimethyl maleate, diethyl maleate, diallyl maleate, dimethyl fumarate, dimethallyl fumarate and diethyl glutaconate;

(4) Organic nitriles such as acrylonitrile, methacrylonitrile, ethacrylonitrile, crotonitrile, and the like;

(5) Acid monomers such as acrylic acid, methacrylic acid, crotonic acid, 3-butenoic acid, angelic acid, tiglic I acid and the like;

group and preferably the latter will be attached to a negative radical such as a benzene ring, a chlorine atom,

- an ester linkage, a nitrile group or the like. They should idene chloride), bromoethylene, fluoroethylene, iodoethyl- 1 ene, 1,1-dibromoethylene, 1,l-difiuoroethylene, 1,1-diiodoethylene, and the like;

(3) Esters of organic and inorganic acids such as vinyl acetate, vinyl propionate; vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl caproate, vinyl enanthate, 1

vinyl benzoate, vinyl toluate, vinyl p-chlorobenzoate, vinyl o-chlorobenzoate, vinyl m-chlorobenzoate and similarv vinyl halobenzoates, vinyl p-methoxybenzoate, vinyl omethoxybenzoate, vinyl p-ethoxybenzoate, methyl methacrylate, ethyl methacr late, to l methacr late, bu l V y P W y ty of about 120 C., At these temperatures the System methacrylate, amyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, decyl methacrylate,. methyl crotonate, ethyl crotonate and ethyl tiglate, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, amyl acrylate, hexyl acrylate, 2-ethyl-hexyl acrylate, heptyl acrylate, octyl acrylate, 3,5,5-trimethylhexyl acrylate, decyl acry late and dodecyl acrylate, isopropenyl acetate, isopro-j penyl propionate, isopropenyl butyrate, isopropenyl isobe free of carbon-carbon conjugated double bonds.

' The monomer component, or components may be em-' ployed over a relativ ely broad range, but usually, the proportion thereof upon a weight basis will be less than the polyester component. Usually, the percentage of monomer will fall within a range of about 10 to 45 or 50 percentby weight of the total mixture of polyester and monomer. The preferred range of monomer is about ""20 to 40 percent, in most instances.

Since the polyester component is usually highly viscous oreven solid at normal atmospheric temperatures, it is preferred to add the monomer to the polyester when the latter is heated to or above the fusion temperature. Normally, the temperature of addition of monomer will be above 100 C and may conveniently be at a temperature polyester and the monomer are highly reactive even in butyrate, isopropenyl valerate, isopropenyl caproate, isopropenyl enanthate, isopropenyl benzoate, isopropenyl pchlorobenzoate, isopropenyl o-bromobenzoate, isoprQ- the absence of catalysts of addition reaction such as benzoyl peroxide or other free radical initiators. Accordingly, it is preferred to effect the mixing operation while one or both of the components contains a gelation inhibitor such as one of the quaternary ammonium compounds selected from the following list disclosedin the fo eg i P tent to E l E- -1 V .1

TABLE- TB.

Tfimethyl benzy m m acetate Trimethyl benzyl ammonium chloride T t yl nzi'l am o m b mide T riethyl'benzyl ammonium chloride Tripropyl benzyl ammonium chloride Tributyl benzyl ammonium chloride.

etyl trimethyl ammonium chloride 'Octadecyl trimethyl ammonium hloride Trirnethyl benzyl ammonium chloride Lauroyl pyridinium chloride h nyl me hyl a monium chl ride Tolyl trimethyl ammonium chloride Benzyl trimethyl ammonium phosphate Benzyl trimethyl ammonium iodide Ethyl pyrodinium chloride Bhenyl trimethyl ammonium chloride Qflyl rim thyl ammon uin bromide Ethylene bis (pyridiniurn chloride) .Ethylene bis (-trimethyl ammonium. bromide) Trimethyl benayl ammonium oxalate Trimethyl benzyl ammonium maleate Trimethy benzy a m n m rtra e Trimethyl benzyl ammonium'lactate Trimethyl ben zyl ammonium chloride D s bu y p oxyho yy d m t benay nium chloride Other inhibitors which may be soused, include1phenolic compounds such as hydroquinone, -p-behzoquinohe; tertiary butyl catechol, S-isopropyl' cate'cho'l, 4-isopropyl catechol and others. These inhibitors maybe employed in amounts Ieifective to prevent prem'a-ture gelation-to a reasonable degree. Excesses may be employed, but 'na t- Wally y increase Costs i l' curing l fi .35 to impregnate :fabricsxsuch as *fabrics of glass orof ortive amounts, of course, will depend upon'the reactivity of the polyestermonomer systems, "thefpotency of'the inhibitor and such like factors. Usually the inhibitor. need not be empolyed in an amount in excess of *1 percent by weight based upon the interpolymerizable components employed. In most instances the inhibitor" should be employed in an amount above about 0.00'1 percent by weight upon a like basis. i i V it will be appreciated that esters .Of salicylic acid themselves often have some efi'ect as inhibitors of gelationand for that reason,- it is sometimes permissible to reduceflthe proportion of the conventional gelation inhibitor {in the interpolymerizable mixture substantially below the amount which would be required in the absence .of esters of salicylic acid. i

The stabilizeragainst'discoloration by light 'euehies the phenyl ester of salicylic-acid may be added QtoQthe interpolymerizable mixture at the time that thelatter is formulated, or itmay be added to acomponents ugh as the polyester component before the addition cflthe monomer. As previously indicated, the sa cylic ester is soluble in the interpolymeri zable"mixturelorfthepoly.

ester component even atnormal room temperatures and may be added to the mixture at any stageofistqrage before the mixture is actually subjectedito jinterpgl ymerization Jnte ndy er mbk m x ures-rat zPQlYQSlQES and mono:

6 more zeoutaininga smallamo'unt ofaasalicylic ,acidhster suchsasnphenyl salicylate taddedaatnany desired stage 40a component: ofzthe mixture, either. hotoracold, or to :the mixture: during. aor subsequent tov its spreparation, .can-rbe .5 stored"tor uses-as .adesired. :lNhen 'the :mixture to be employed inqthe preparation; of .castings, laminates, vor similar aarticlesmitis preferred to add a :catalyst such as one ofihe ifree'radicaliinitiators andbeing represented by henzoyl uperoxide, itertiary butyl phydroperbxide, cyclo- 10 hexyl =hydroperoitide, acetylperoxide, cumenmhydroperoxide, and many .others. :Soluble .salts ,of. cobalt, lead, manganese, mickel and many zotherasimilar ,metalsi-are oiten; employed @with thezcatalysts as 1 promoters of free radical formation. The naphthenates, linoleatesandtsuch like salts ;of-;the metalsswshich are soluble:imthepolyesters i Amounts of approximately 0.1tb- 3",perc.ent,by ,weight of the free radical initiator are deemed .t-o be especially ef- 'fective ilfhe interpolymerizahle mixtu-res of polyesters containing the alpha betagroup and the monomers-containing G ="(3Hzgr0ups andcontaininginhibitors of gelation a 's -well-as {phenyl s'alicylate and'ifree radical initiators, in accordance -with theiprovisionsb-fthe present invention, can rea dil-y be-poured into molds sin ce they ere normally liquid homogenqus mixtures. Theycan al'so be employed ganic mater ials e. g., cotton or=the like. lkhey may also 'be em-ployed to impregnate -bets and p'ref orm s of-heterogeneously disposed fibers. I "The'mixturesin molds, or-on -fabrics, or supported in ii) any othereonvenientwaymay be caused to undergo rapid interpolymerizatiori, or curing-bythe-applicatio1i of rela- -tively mild-heat, for example, a temperature of about 75 td-150 C. or thereabouts. In most instances, -tempera'- t-ures of about 90 i C. to -1Q0 Clare quite effective in pmducinggel ling and ultimate curing of the mixtu'restojhard resinous state. The' timerequired for curing will vary greatly, dependent upon the reactivity Y of the polyestermonomer-mixture;=the activity of the catalysts or h'ee radical initiator, the gelat-ion inhibitor-and the amount thereof, the temperature of interpplymerization, and the thickness ofthe body ofthe mixture-to-be cured Usually, :thecures can be eifeetedwithin a period of a'few minutes, c. g.,=20r*3 minutes.to l-or- 2 hours. I f desire d,fthe-mixture s, on-the :boldies containing-the mixtures, can betc u'red '-in two stages; In thefirst 'stage, cure is efi ected with or without a moldyas may be requiredgand at a moderate temperature, e. -g., 99 to 100 9 {C2 to provide self-supporting body whichisilltimately hardened by abaking operation in an oven at a temperature of about to C. A

=60 convenient baking schedule involves a time cycle of 5 or .1 0 ,minutes to about Lhoursdependentupon thesize of gthe ,article do be =,-finished, :hgardness desired ;and ;other itaq o s- The .in terpolymer-izable.mixtures of this invention con- 435 g-t-aining a salicylic acid ester as ;an inhibitor of, discoloration rr ray be employed- 1to prepare clear castings useful-as-ob- ,ajects :Ofyfili, e. g, asefigurines, ornaments, or.-the1like. ,They may also ;.be used as aem-bedment media for J protectively embedding flowers, biological specimens, :keep- .sakesand; numerous othenarticles. Still other uses involve linean-form llsefulr-fcnglazing purposes such as in automoi-biles, trains, rboats, i airplanes :and'. the :li-ke. 'The bod-ies containing reinforcing-.inaterials.suchras. glass fibers, cotton #16 Qfibers, .orjanyzsother- .rsimilar"; materials may I be used :as

.thegcasting .ofthin,':transparent sheets in Lplanar or .cu-rvalaminates, for example, in instrumentpanels used in the construction of automobiles, airplanes or as wing coverings and such likepurposes. In the transparent articles, the interpolymers retain their high clarity and freedom from yellowing or other discoloration remarkably well, even when the articles are subjected to relatively high intensities of ultra-violet irradiation. The reinforced plastics usually are lacking in transparency; but the freedom from discoloration often is desirable for esthet-ic or other reasons.

It Will be apparent that the uses of the interpolymerizable mixtures above discussed are merely by way of suggestion. These constitute only a few of the numerous applications to which the materials are susceptible of .application. f

Illustrations of the use of the phenyl ester of the salicylic acid known commercially as Salol as an inhibitor of discoloration are contained in the following examples:

Example I The interpolymerizable mixture of this example comprised a product containing a polyester obtained by the reactionof:

Component: Moles .Maleic anhydride 4 'Phthalic anhydride '6 Propylene glycol 11 The mixture was cooked under an inert atmosphere and 0.1 percent by weight based on the above mixture of trijphenyl phosphite (an optional ingredient) and hydroquinone (0.01 percent by weight based upon the above mixture) was also added. The mixture was cooked until water ceased to evolve and an adequate viscosity was attained. This polyester, in a proportion of 65 parts by weight, was mixed with 35 parts by weight of styrene. A control sample of this material was prepared and to it was added 0.3 percent by weight based upon the total mixture of tertiary butyl peroxide.

-A second sample of the same composition contained 1 percent by weight (based upon the total composition) of phenyl ester of salicylic acid. The latter could be added to hot or cold mixtures. Both of these mixtures were poured into molds designed for the casting of resinous sheets and were cured at 170 F. until a solid resinous product was obtained. The sheet was further baked at 220 F. until the surface was hard and mar-resistant. These two products were transparent and of the type em, ployed in airplane glazing and such like operations.

For purposes of determining their resistance to discoloration upon aging, they were subjected to a severe test inno inhibitor of discoloration had a color index of 48. In t the color scale, reduction of the number indicates an improvement in color. Therefore, phenyl salicylate was shown to be an efiFective inhibitor of discoloration.

Example II In this example, an interpolymerizable mixture comprising 1 part by weight of styrene and 2 parts by weight of a polyester of 2 moles (or a slight excess thereof) of propylene glycol, 1 mole of maleic acid and 1 mole of phthalic acid was prepared. The mixture was stabilized against premature gelation with 0.1 percent based on the polyester of trimethyl benzyl ammonium chloride and 0.005 parts by weight based on the total composition of quirione, and 0.1 part by weight of triphenyl phosphite. The mixture was divided into a series of samples, one of which was employed as a control without added color inhibitor. To a second sample was added 1 percent by weight based upon the polyester component of phenyl salicylate and to a third sample was 0.5 percent by weight of. the same material. These additions were of- 8 fected while the polyester was at a temperature of 285 F. However, the additions could be effected while the mixtures were at normal room temperature with little efiect on the results. These samples were stored for a period of 1 month and at the end of this time, 1 percent by weigh-t based upon the interpolymerizable mixture of benzoyl peroxide was added. The mixtures were placed in molds and cured into sheets as in the preceding example.

The resultant sheets were then subjected to the conventional ASTM weathering tests in the so-called Weather- O-Meter and were exposed for periods respectively of 200, 500 and 1000 hours to irradiation by ultra violet light. The color index of the samples per centimeter of thickness was determined .and the readings are respectively as follows:

The tests clearly indicate the elfect of phenyl salicylate as an inhibitor of discoloration of the compositions. The composition so inhibited would be valuable in the preparation of plastic sheets for glazing airplanes. The several examples are by way of illustration.

' It will. be apparent that in these examples, other polyesters of alpha-beta ethylenic dicar-boxylic acids, and other monomers may; be substituted for those specifically referred to. For example:

In the polyesters, glycols such as diethylene glycol, polyethylene glycol or the like can be employed. Maleic acid can be replaced by fumaric acid or itaconic acid; phthalic acid-can be eliminated, or replaced by sebacic or adipic, or other dicarboxylic acid in molecularly equivalent amount. Various monomers such as vinyl acetate, vinylchloride, methyl methacrylate, diallyl ph-thalate and many others, may be substituted in part or in toto for styrene. Phenyl salicylate may be replaced, in the preceding examples, by methyl salicylate, ethyl salicylate, diis'opropylene glycol salicylate, isoamyl salicylate, isobutyl salicylate, tolyl salicylate, xylyl s'alicylate and others, though the phenyl salicylate is presently preferred.

These and many other modifications of the invention will be apparent to those skilled in the art as being embraced within the scope of the following claims.

I claim":

l. A hard resinous product having a high color stability and comprising an interpolymer of (A) a polyester of a dihydric alcohol and an alpha-beta ethylenic dicarboxylic acid (B) a monomer containing a C=CH2 group and (C) an ester ofs'alicylic acid said ester being incorporated in the interpolymer.

2. An interpolymerizable mixture of (A) a polyester of a dihydric alcohol and an alpha-beta ethylenic dicarboxylic acid (B) a monomer containing a C=CH2 group and (C) an ester of salicylic acid and a phenol said ester being in solution in the mixture.

3. An interpolymerizable mixture of (A) a polyester of a dihydric alcohol and an alpha-beta ethylenic dicarboxylic acid (B) a monomer containing a C=CH2 group and (C) phenyl salicylate, said phenyl salicylate being employed in an amount to impart color stability to the interpolymer of the mixture and being in solution in the latter.

4; In the method of imparting color stability to an interpolymerizable mixture of (A) a polyester of a dihydric alcohol and a carboxylic acid .at least some of which contain'salpha-beta ethylenic unsatura'tion and (B) a monomer containing a C=CH2 group, the step of adding to said mixture a small stabilizing amount of an ester of salicylic acid said ester being in solution in the mixture. v

5. An interpolymerizable mixture of (A) a polyester of a 9 a dihydric alcohol and a mixture of dicarboxylic acid one of which is alpha-beta ethylenically unsaturated and the second of which is free of such unsaturation (B) a monomer containing a C=OH2 group and (C) an ester to discoloration by irradiation, the steps of forming a liquid mixture of (A) a polyester of a dihydric alcohol and an alpha-beta ethylenic dicarboxylic acid (B) a monomer containing a C==CH2 group (C) phenyl sal-icylate (D) a peroxidic free radical initiator (E) a soluble salt of metal which is a siccative for drying oils, and heating the mixture to cure the same to hard resinous state.

References Cited in the file of this patent UNITED STATES PATENTS 2,627,510 Parker Feb. 3, 1953 Bjorksten et a1 Nov. 11, 1952 

1. A HARD RESINOUS PRODUCT HAVING A HIGH COLOR STABILITY AND COMPRISING AN INTERPOLYMER OF (A) A POLYESTER OF A DIHYDRIC ALCOHOL AND AN ALPHA-BETA ETHYLENIC DICARBOXYLIC ACID (B) A MONOMER CONTAINING A >C=CH2 GROUP AND (C) AN ESTER OF SALICYLIC ACID SAID ESTER BEING INCORPORATED IN THE INTERPOLYMER. 